Ultra high frequency wavemeter



April 11 1950 E. GlNz'roN ETAL 2,503,256

ULTRA HIGH FREQUENCY WAVE METER Filed Jan.. 29, 1943 Y 4 Sheets-Sheet 1 ATroRNEY E. L. GINZTON TAL ULTRA HIGH FREQUENCY WAVE METER April 11, v195o Filed Jan. 29, 1943 DIA/M5752.

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ULTRA HIGH FREQUENCY WAVE METER 4 sheets-sheet s Filed Jan. 29, 1943 QE Il .Qw\\ \\v\ kmQ @mi INVENTORS E L GINZTON F. L. SALISBURY Alli Mg 1950 E. l.. GlNzToN ETAL lULTRA HIGH FREQUENCY WAVE METER 4 Sheets-Sheet 4 Filed Jan. 29, 1943 fll INVENTORS E .GINZTON BYl F. SAL|SBURY ATTORNEY Patented Apr. 11, 195o I ULTRA HIGH FREQUENCY WAVEMETER Edward L. Ginztn, wantagh, and Frederick L. Salisbury, West Hempstead, N. Y., assignors to The Sperry Corporation, a corporation ol' Dela- Ware Application January 29, 1943, Serial No. 474,016

2 Claims.

This invention relates to ultra high frequency electrical apparatus and more particularly to energy leakage prevention arrangements for use in Wavemeters and the like having relatively adjustable surfaces enclosing or conducting ultra high frequency energy.

In its preferred embodiment, the invention will be described as incorporated in a Wavemeter although certain principlesmaybeextended to other devices as will appear. More speciilcally the invention contemplates the provision of wave trap arrangements for preventing leakage of ultra high frequency energy between relatively adjustable surfaces in wavemeters and other ultra high frequency apparatus.

For example, in wavemeters of the concentric line or cavity resonator type prior to the inven= tion, coextensive surfaces of the adjustable plunger or piston and the adjacent surfaces of the meter have usually comprised such devices as ball bearings, spring ilngers or the like seeking to maintain maximum physical contact between the surfaces in all positions of tuning adjustment. Such arrangements have not proved satisfactory i or preventing leakage of ultra high frequency energy at the joint between the relatively adjustable surfaces, besides being stiff and diiiicult to uniormly adjust because of the high friction between the parts.

1t is therefore a major object of this invention to provide ultra high frequency apparatus wherein novel arrangements are provided between relatively adjustable or like movable surfaces enclosing or conducting ultra high frequency energy, for preventing undesired leakage oi energy through the joint between the surfaces. Preferably an impedance-transforming coupling of predetermined characteristics is provided between `the surfaces.

A further object of the invention is to provide i novel wavemeter construction wherein undesired leakage of ultra high frequency energy is pre vented. The wavemeter may be ofthe concentric line type or the cavity resonator type, either type having relatively adjustable members denning a joint at which leakage is to be prevented.

A further object of the invention is to provide novel crystal detector arrangements in an ultra high frequency wavemeter.

Still a further object of the invention is to provide a novel wave trap construction between relatively axially adjustable parts of a coaxial type transmission line.

A further object of the invention' is to provide novel scale arrangements for une adjustment wavemeters.

It is a further object of the invention to provide novel wavemeter construction operable for substantially directly :measuring wave length oi radiation in wave guides.

A further object of the invention is to provide novel wave trap arrangements for preventing leakage of ultra high frequency energy through the joint or `joints between two relatively adjustable surfaces in a wavemeter or the like.

Further objects of the invention will appear as the description proceeds in connection with the appended claims and the annexed drawings wherein:

Fig. 1 is an elevation, partly in section, ci a concentric line type wavemeter embodying the invention;

Fig. 2 is an end elevation, partly broken away to show the interior, looking from left to right in Fig. l;

Fig. 3 is a bottom plan view of the wavemeter.

of Fig. l;

Fig. 4 is a partly sectional view illustrating a further embodiment'of a concentric line type wavemeter of different internal construction;

*Y Fig. 5 is a fragmentary sectional elevation il lustrating an alternate output connection and. crystal detector mounting which may be used with Fig. 1 or in any of the forms of the inven- Fig. 6 is a side view, partly in section, of a wavemeter of the cavity resonator type designed to operate in a selected mode and utilizing the principles of the invention;

Fig. 'l is a section along line -i of Fig. 6;

Figs. 8, 9, 10 and ll are diagrammatic views illustrating the electrical and magnetic field distributions according to a preferred .mode oi oscillation of the wavemeter of Fig. 6;

Fig. l2 is a side View, partly in section, illustrating a wavemeter operating similar to Fig. l but of slightly diiierent construction;

Fig. 13 illustrates the invention as applied to a coaxial line adjustment assembly;

Fig. le is an end elevation of the apparatus of Fig. 13.

Fig. l5 is a plan view, partly in section, of a further embodiment of the invention embodying awide range meter having a, special scale assemb y;

Fig. 16 is a front elevation oi the meter of Fig. l5;

Fig. l? is a fragmentary end view or the rear face of the scale plate of Fig. 15

Fig. 18 is a sectional view illustrating the invention as embodying an adjustable piston slidable in a continuation of a rectangular Wave guide.

Figs. 19 and 20 are sections along lines ill-iii and 20-20 of Fig. 18; and

Fig. 21 is a. sectional view illustrating the principles of the invention as applied to an adjustable wave guide plug.

Referring to Fig. 1, a metal wavemeter body iii of any desired external shape is formed with an internal cylindrical bore II enclosing a chamber I2 bounded at opposite ends by a removable iiat wall I3 and a metal partition I4 parallel to wall I3, and both wall I3 and partition I4 are perpendicular to the axis of bore II.

Partition I4 is rigidly fixed in an internal shoulder I5 in the resonator body and, beyond partition I4, body I is formed with a reduced cylindrical bore I which extends to an integral end wall I1 parallel to Wall I3. Thus, partition I4 separates a pair of right cylindrical chambers. and the relative diameters of these chambers are not material to the invention.

Partition I4, which may be integral with body Il if desired, is centrally apertured and formed with an integral hollow sleeve I8 which in Fig. 1

' projects into both chambers, although the exact extent to which it projects into either chamber is not critical as will appear later in discussing the critical factors related to the meter dimensions.

A cylindrical rod I9, which may comprise an extension of a micrometer plunger as illustrated, extends coaxially through sleeve I8 and projects therebeyond into chamber I2. The outer surface of rod I9 is exactly parallel to but spaced a predetermined small distance from the interior surface of sleeve I8 over their coextensive length, so that rod I8 and sleeve I8 dene an impedancetransforming coupling between the relatively movable parts of the wavemeter, as will be explained. Wall I1 is formed with an apertured hollow boss 2I in which is non-rotatably secured, as by setscrew 20, a micrometer barrel 22 rotatably carrying the micrometer spindle 23. Spindle 23 is formed with a reduced portion 24 on which is snugly frictionally fitted a hollow tube 25 extending through sleeve I8. If desired, rod I9 may be a continuous solid or hollow member rigid or integral with spindle 23. The externally threaded end of boss 2| is provided with a nut 26 for panel tting purposes.

The usual rotatable micrometer handle 21 is mounted on barrel 22, and the barrel and handle are marked with the usual micrometer scales 28. Desired axial displacement of plunger rod I9 within chamber I2 is effected by rotation of handle 21 in either direction, and the amount of this displacement is indicated by scales 28. Since such micrometer construction is well known, further description of this part is not necessary.

An aperture 29 is formed in the wall of bore II adjacent partition I4 for rigidly mounting a hollow pipe fitting 3i carrying a coaxial hollow tube 32 adapted to telescope with the outwardly projecting terminal 33 of a stiff wire loop 34 disposed at least partly within chamber I2. Fitting 3|, 32 and wire 33, 34 comprise a concentric line and antenna coupling for introducing the ultra high frequency energy, the wavelength of which is to be measured, into chamber I2 of the wavemeter. Any equivalent transmission line such as a wave guide may be employed for the same purpose. Fitting 3| is suitably threaded at 35 for attachment t0 an input transmission line.

Bore II is formed at another region adjacent' partition I4 with an aperture 36 in which is rigidly seated tubular metal pipe fitting 31 externally threaded at 38. Fitting 31 is formed with a cylindrical bore into which extends a crystal detector cartridge 39. Cartridge 39 externally comprises a metal base 4I having an enlarged head 42, a porcelain or like insulator body 43 and a metal terminal 44. A sensitive crystal, of silicon or the like, is mounted in solid contact within base 4 I and a cat's Whisker wire connected 4 at one end to terminal 44 has its other end in contact with a sensitive portion of the crystal, the crystal and wire being held immovable by imbedding insulator material. This cartridge per se is of known construction, so that further description is not necessary.

Cartridge 39 is frictionally fitted into a supporting annular insulating sleeve 45 which electrically insulates the cartridge from iltting 31, and which serves as the dielectric of a by-pass condenser arrangement for the alternating component of the rectified current. This prevents leakage of high frequency energy past the cartridge.

An externally knurled metal tube 46 is threadedly connected at 38 to fitting 31. Tube 46 carries a conductor terminal 41 fixed in an insulator block 48 which is held against axial displacement in the tube, as by shoulder 49 and a snap ring and groove 5I. A spring 52 is compressed between the enlarged inner end of terminal 41 and cartridge head 42, when tube 46 is drawn up tight.

A suitable spring finger 53 anchored at one end to partition I4 serves for coupling the interior of chamber I2 to terminal 44. Thus finger 53, terminal 44, the wire and crystal within cartridge 39, base 4I, head 42, spring 52 and terminal 41 comprise one conductor of the output line, of which tube 46 is the other conductor. A suitable coupling 54 is provided for leading the output to a milliammeter or other indicator as indicated.

In operation, the ultra high frequency energy to be measured is introduced by the input line and loop 34 into chamber I2, where standing waves are set up. To determine the frequency of these standing waves, we axially adjustplunger rod I9 through manipulation of rotatable handle 21 until the indicator connected to the output line shows a maximum reading. This occurs only when the chamber I2 is of such dimensions as to be resonant at the input frequency. From the micrometer reading at resonance, the wavelength of the input energy may be calculated if the meter has been previously calibrated. If desired, the scales 26 may read directly in wavelength or frequency.

Referring now to Figure 1, the distance from point 55 to partition I4, as measured through the space between sleeve I8 and bore I6, is preferably chosen as substantially electrically equivalent to one-quarter of the average resonant wavelength in the range for which the wavemeter is designed. For example, the -particular wavemeter shown in Figure 1 has a measurement range of 8.5 to 12.5 centimeter wavelengths which means it may be adjusted to produce resonance in chamber I2 Vat any wavelength in that range. A good choice for the working quarter wavelength distance would therefore be one-quarter of the average 10.5 centimeter wavelength.

Again, the wave meter shown in Figure 15 has a range of only 3.1 to 3.4 centimeters. The quarter wave distance which can be selected for the capacitative coupling in such a small range meter will of course lie in a smaller range than the larger range meter of Figure 1, but in both meters the available range is suiiiciently small that the small differences in quarter wavelength of the frequencies in the operative range may be considered negligible as a practical matter.

It will be understood, however, that this preferable working quarter wavelength distance is not essentially critical within practical considerations. The wavemeter has a relatively small alicante we will refer herein to this working distance as substantially a quarter wavelength of a frequency within the operative range of the. wavemeter, and we intend to embrace any substantially equivalent distance equivalently effective for the purpose below explained over the wavemeter range. Y

Thus, from point 55 to partition il we have a substantially quarter wave line short-circulted at one end, so that the impedance at point 55 looklng toward partition I4 is very high, nearly infinite. We also choose the length of sleeve i8 to be equal substantially to a quarter wavelength of a frequency in the operative range of the wavemeter. Since the impedance at point 55 is very high, the impedance at point 55 looking toward point 55 at the other end of that quarter wave line section is transformed to a very low value.

This arrangement provides the equivalent of a direct electrical short circuit between sleeve I8 and rod i8 at point 55, so that sleeve i8 and rod i5, although relatively movable, are electrically interconnected more eiliclently than by the best known possible friction joint. This eilicient electrical connection is, moreover, mechanically frictionless, so that adjustment of plunger i8 is rendered smooth and even.

We have thus provided an eil'ective half wavelength trap continuously eective for blocking escape of energy from chamber i2 regardless of the position of adjustment of rod i8. Ihe coextensive length of sleeve i8 and rod i8, and the electrical distance between point 55 and partition il remain unchanged during all adjustments of rod i8 in the wavemeter range.

The wavemeter of Figure 4 differs over that of Figure 1 chiefly in the wave trap construction. The wavemeter body 55' encloses a cylindrical bore 55 separated into two chambers by a partition 51. A cylindrical sleeve 58, integral with partition 51, extends into the resonant chamber 58 in closely spaced relation to axially adjustable rod i8. End wall Si mounts the above-described micrometer structure, as well as a. rigid sleeve 82 vcoaxial with rod i5 extending toward partition y 51. Sleeve 52 terminates short of partition 51 to provide a gap indicated at 88.

The distance electrically between point 85 and wall 8|, and the length of sleeve 58, are each chosen as substantially one-quarter wavelength 'of a frequency within the operative range of the wavemeter, as in Figure l. Thus, looking to the right in Figure 4, point 55 is of nearly inilnite impedance and substantially zero current, so that point 64, coupled thereto by a quarter-wave transmission line, has very low impedance.

Thus we provide an effective half wavelength wave trap between point 5l and wall 8i which prevents appreciable escape of energy from chamber 58.

The wavemeter of Figure 4 operates similarly to that of Figure l, and the two embodiments demonstrate that gap 58 may be located anywhere between partition 51 and wall 5I, provided of course the wave trap characteristics are maintained.

Figure 5 illustrates an optional form of deln'l'lgul'ellfdeslred. Tubeisthreadedto pipe mung es which a the same as stung a1 `choice of the absolute value of this distance and except for thecartridge mount. An annular metal collar 1i having a bore 12 larger than cartridge base Il, and a smaller bore 18 snugly iltung porcelain body'u is rigid orv integral with fitting 58. A relatively stiiI wire 14 is xed at one end to the wavemeter body wall and bent at right angles to coaxially enter iitting 88, within which it ends in an enlarged head 15 telescoping terminal M. Y

Wire 14 is suillciently rigid to prevent the cartridge from being advanced by spring 52 beyond from the partly coextensive bore 12 and defines therewith a by-pass condenser arrangement similar to Figure 1. An advantage of this structure is that insulator sleeve I5 of Figure 1 is unnecessary, the air space between bore 12 and base 4I serving as the dielectric of the condenser.

Figure 6 illustrates a cavity resonator type wavemeter embodying the principles of the invention. Wavemeters similar to those shown in Figs. 6 and 12 are claimed in application Serial No. 102,276, iiled June 30, 1949, a division of the present application. 4A tubular body member 16 having a cylindrical bore 11 is closed at one end by an integral wall 18 and at the other end by a removable wall 18 secured as by screws 8i to the member 15. A spindle 82 is formed with a section 88 rotatably mounted by means of a relatively i'lne thread connection in wall 18. A micrometertype barrel 8| is fixed to the outer end of spindle 82 and carries a scale 85. A stationary micrometer-type barrel 85 having a scale 81 cooperating with scale 85 is rigid with body member 16.

A piston memberl 88, eiectively comprising one end wall of the resonant chamber 88 otherwise.

dened by bore 11 and wall 18, is mounted on the inner end of spindle 82. The piston is formed with a thin rearwardly extending side wall 88 parallel to but spaced from the coextensive porhere also we have provided a half wavelength wave trap at the piston. The impedance at point 8i is very low according to the explanation above in connection with Figure l, so that the coupling represents an effective electrical short circuit between the piston and bore.

Piston 93 is preferably a duplicate of piston 88 and has a side wall 84 also substantially onequarter wavelength in length which forms a wave trap functioning similarly to that at piston 88 for blocking escape of any high frequency energy which might pass beyond piston 88.

In operation, chamber 88 is ucited by introduction of ultra high frequency energy to be measured thereinto, as by the rectangular wave guide 95 and communicating aperture 95 in wall 18. Preferably, where chamberii is cylindrical. the exciting energy is so introduced with the electrical lines` of force oriented as in Figure 6 so as to set up an oscillating ileld having generally the mode shown in Figures 8-11. In this mode, the electrical ileld represented by lines E is strongest adjacent the axis of chamber 88, while the magnetic ileld represented by the lines B is strongest tector cartridge mounting which may be used 75 adjacent the chamber side wall. The graphs of energy.

7 Figures 9 and li represent the electric and magnetic ileld distributions E and B in the illustrated cross sections.

As barrel 84 is revolved, piston 58 is displaced along the axis of bore il to change the dimensions or chamber l until chamber ll is of such size as to ronate at the frequency oi' the input The condition of resonance is detected as by an output line like that in Figure 1. Scales 85 and 81 may be read and related to a suit-v able calibration chart, or may be graduated to read directly in terms of wavelength. 'I'he wave traps at pistons 88 and 93 maintain their operational chamcteristics during all positions oir adjustment oi.' the pistons and therefore function to prevent energy leakage from chamber 88 in normal wavemeter operation.

The output line for detecting the resonant condition within chamber 80 may be the same as shown in Figmes 1 or 5.

The wavemeter illustrated in Figure 12 is very similar to that of Figure 6 but is of larger dimensions and measurement range. Body 51, which also serves as the stationary micrometer barrel,

. cured to the outer end of a spindle |85 rotatably moimted by a relatively coarse thread in wall lli. Pistons |54 and |55, which are shaped to deiine half-wavelength wave traps preventing unwanted escape of energy from cylindrical resonant chamber |55, are dimensioned similarly to the piston in Figure 6. Walls |01 and |58 are thus each substantially equal in length to aquarter wavelength in the resonant range of chamber |85.

Chamber |85 is much larger than chamber 80 in Figure 6 and measures longer wavelength energy over a. somewhat larger range. 'I'he wavemeter of Figure 12 has an output detector line similar to that in Figures 1 or 5 and otherwise operates similarly to Figure 6.

Figure 12 also illustrates a stationary wave trap in the coupling between input wave guide sections |85 and Sections |09 and have coupling iianges rigid therewith and secured together rigidly so as to slightly space their opposite ends as at point I IZ. Internally, coupling ||l b formed with a passage H3 open at one end at point ||2 and at its other end to a blind passage ||4. Each of passages ||3 and ||4 is of a length substantially equal to one-quarter of the resonant wavelength of the energy normally carried by the .wave guide, as indicated. 'I'he wave trap defined by passages ||3 and ||4 prevents energy leakage from the wave guide.

Figures 13 and 14 illustrate the invention as applied to an adjustable concentric line coupling which may be employed as at aperture in Figure 1 as shown, or as the input line for the wavemeter of Figures 6 or l2. Outer conductor H5 carries a coaxial inner conductor H6 formed into antenna loop ||1 within the chamber `|2. Conductor ||5 is axially' slidably but non-rotatably mounted ima bearing support provided by boss ||8 integral with body Boss ||8 carries a pinion I l5 adjustable by knob |2| and cooperating with a. rack |22 on conductor ||5 for axially shifting the conductor. This axial adjustment may be locked at any point as by a screw |23 cooperating with a split section of boss I I8 as illustrated.

Boss ||8 is internally formed with an enlarged cylindrical bore |24 terminating in 9, wall |25. A

8 jects outwardly in coaxial spaced relation to conductor ||5. but terminates at a gap |21 short of wall |25. As indicated in Figure 13, the length oi' sleeve |28 coextensive with conductor ||5 is substantially a quarter-wavelength of a frequency within the operative range of the meter or oth device with which it is employed, and the distance from gap |21 to body through the space between bore |24 and sleeve |25 is also electrically substantially equal to a similar quarter-wavelength, thus providing a half wave trap eiiective during all conditions of adjustment of loop ||1 for varying input coupling with chamber I2. The

adjustable assemblage oi' Figure 13 therefore opcrates similarly to that of Figures 16 and 12.

' Figures 15-17 illustrate a further form oi' the cavity resonator type wavemeter having a relatively iine adjustment over its range. Here pistons |28 and |25 similar to pistons |54 and |85 are secured upon a spindle ill having a threaded connection at |32 to a body |38 which is ilxed to a panel |84 as by screws |35. The output line at is the same as in Figure 5, while the input line is a conventional coaxial line and loop antenna |85.

A scale disc |31 has a spiral scale |38 marked, for example, thereon in the range of 3.100 to 3.400 centimeter wavelengths. Such an effectively long scale enables us to employ relatively iine threads at |32 which increases the accuracy of the meter. Disc |31 is removably mounted on spindle |3i, as by the releasable clamp ring |35, so that dif-'- ferent scale range discs may be substituted. The disc and spindle are rotated as a unit by knob |45.

An index plate |4| having a window |42 and Vernier markings |42 is mounted as at |44 for sliding movement radially of disc illgalong a support |45 iixed to panel |34. Plate |4| is formed with a projection |45 arranged to track within a spiral groove |41 on the back of disc |31 coextensive with scale |38. As knob |45 is rotated for changing the dimensions of the resonant chamber, window |42, which is of such size as to frame the working section of the scale, is continually radially positioned to follow the scale. This scale arrangement permits relatively fine ad- .iustment in a. wavemeter. which otherwise is constructed and operates similarly to the wavemeters in Figures 6 or 12.

Figures 18-20 illustrate the invention as applied to a wave guide terminal which may serve as part of a wavemeter.

A rectangular wave guide |48 which is supplied with energy as adjacent its other end (not shown) has a partition |49 formed with an aperture |5|. Beyond aperture |5I, rectangular pistons |52 are mounted on a shaft I 53 rigid with a rectangular block |54 slidably iitted within guide |48, the whole constituting a slidable piston assembly. The piston assembly, as illustrated, is provided with the same impedance-transforming coupling with guide |48 as explained above in connection with Figures 6 and 12.

Shaft |53 extends ilxedly through block |54 into threaded engagement with a rotatable wedge handle |51 which has a conical face |55 disposed within a similarly shaped depression in block |54. A locking key |58 is mounted for radial sliding movement in a suitable aperture in block |54 and has an inclined face adapted to contact face |58. When handle |51 is rotated in one direction, it advances along shaft |58 toward block |54 so that face |58 wedges key |55 outwardly against the inner surface of guide |45 to thereby thin cylindrical sleeve |26 rigid with body pro- 75 lock the whole piston assembly against axial sliding along guide |48. When handle |51 is rotated to loosen key |59, the entire piston assembly may be slidably displaced along guide |48.

When used as a wavemeter, the piston assembly may be measurably displaced along guide |48 and a suitable indicator employed to detect the positions of maximum voltage, whereby the distance between wave crests in the chamber |60 may be measured. Scale and index means for measuring the actual displacement of the piston assembly may be provided on handle |51 and wall |6|. When not used as a wavemeter, the piston assembly may function as a wave guide plug similarly to that in Figure 21. Referring to Figure 21, the piston assembly |52 is shown mounted on a shaft |62 xed to a slidable block |63 Within the open end of a hollow wave guide |64. The front end of the piston assembly is supported on a dielectric slide guide block |65. Shaft |62 extends slidably through rigid end wall |66 so that the piston assembly may be axially displaced as in Figure 18. In Figure 21, the piston assembly functions as simply asa wave guide plug, as for matching v.impedances or otherwise adjustably terminating a wave guide.

As many changes could be made in the above construction and mans7 apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not inv a limiting sense.

What is claimed is:

1. In an ultra high frequency wavemeter, an effective concentric line section comprising outer and inner conductors relatively adjustable axially for tuning, means for loosely coupling an energy source to said line section, said concentric line section being a passive resonator characterized by very high Q, a conductive coupling between said conductors at one region, and a sleeve carried by said outer conductor and surrounding said inner conductor in spaced relation thereto at another region, said sleeve and conductive coupling forming an impedance-transforming' half-wave section for preventing high frequency leakage.

2. A wavemeter for very high frequency energy, comprising a hollow conductive housing transversely partitioned by a conductive diaphragm to form first and second cylindrical cavities each having appreciable volume, said cavities having a common axis.- a tubular conductive sleeve xedly positioned in said diaphragm coaxially with said axis, the outside diameter of said sleeve being appreciably smaller than the inside diameters in said rst and second cavities, a conductive member having a cylindrical outer surface ex` tending axially through said second cavity, onward through said sleeve and beyond the endo! said sleeve in said rst cavity. and part way through said first cavity to end therein and to form a high Q coaxial-line resonator in said rst cavity, the outside diameter of said conductive member being slightly smaller than the inside diameter of said sleeve for high capacitance therebetween, the axial extent of the adjacent surfaces of said sleeve and said conductive member being a quarter-wavelength transmission line of low characteristic impedance at a frequency substantially equal to the frequency of resonance of said resonator, said conductive member and sleeve and the inner cylindrical wall in said secand cavity cooperating as a resonator presenting a high impedance at the end of said quarterwavelength transmission line, coupling means for admitting very high frequency energy to said rst cavity resonator, and means extending external of said housing for adjusting the projection of said conductive member within said rst cavity resonator to adjust the response frequency thereof.

EDWARD L. GINZTON;

FREDERICK L. SALISBURY.

REFERENCES CITED The following references are of record in the ille of this patent:

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